Medical treatment in which a catheter inserted into a blood vessel transcutaneously is led to an internal organ such as a brain, a heart or some of abdominal organs to thus administer or infuse therethrough a proper curative drug, an embolismic substance or a contrast medium has been carried out. In recent years, in view of never-ending progress of medicine, it has become necessary to infuse such curative drug, embolismic substance or contrast medium into still finer peripheral blood vessels and now desired is development of a microcatheter which is capable of insertion into such finer peripheral blood vessels.
With a conventional catheter for infusion, it is a usual practice to have it led to an affected part along a guiding wire preset thereto.
Also developed is a method of making a tip portion of a catheter pliable and, if necessary, bulged so as to make the catheter movable on a blood stream. As a typical example of such catheter is Mallinckrodt Balt Magic Catheter (Trade Name) made by Mallinckrodt Medical Inc.
Meanwhile, as a catheter with a part of its shaft comprising a porous structure, there is exemplified, for example, a catheter with its tip portion made porous lest a blood vessel should be injured thereby, disclosed by Japanese Patent Laid-Open Publication No. 2-142576, an intra-abdominal retention tube made up of a porous part and a nonporous part for the improved adaptability to the form of the abdominal cavity, disclosed by Japanese Patent Laid-Open Publication No. 2-107268 for decreasing a risk of injury to the internal wall of the abdomen when it is retained in the abdominal cavity, a catheter made of polytetrafluroethylene (PTFE) and comprising a porous part and a solid part such that a proper flexibility is attained, disclosed by Japanese Patent Laid-Open Publication No. 60-51912. Also proposed are catheters by Japanese Patent Laid-Open Publication No. 60-129055 and No. 61-247476, each with its normally open tip portion having micro-pores communicating the inside with the outside of a porous tube closed, and when a thrombus-dissolving agent is infused through a proximal portion and the infused agent is caused to be discharged gradually through the side wall of the porous tip portion.
The conventional catheter to be led to an affected part of a blood vessel by the use of a guiding wire is usable without any clinical problem if its outer diameter is relatively large (e.g. 1.5 to 4 mm). Its shaft is however is large in diameter and solid compared with a blood vessel, hence it is rather difficult to insert into fine peripheral blood vessels.
With the rapid development of diagnostic devices such as MRI and CT in the field of neurosurgery, blood vessel diseases (aneurysm, tumor, arteriovenous malformation etc.) in mesencephalic cerebral arteries, basilar artery, anterior communicating artery, posterior communicating artery, anterior cerebral artery, posterior cerebral artery etc. are now readily detectable. Craniotomy of blood vessel diseases in such parts is often infeasible depending on the parts affected due to too high physical burden on a patient or too high probability of complication and operation is possibly infeasible depending on the parts affected. It is, therefore, strongly desired lately to enable insertion of a microcatheter for infusion for detailed diagnosis and treatment. With a conventional catheter which can be readily inserted into common carotid artery, external carotid artery, internal carotid artery etc., it is often difficult to insert it into the peripheral portions thereof, the time required for insertion into such portions is likely too long and often such insertion is infeasible depending on the conditions of a patient.
The catheter moved on a blood stream has its pliable tip portion made of a polyurethane elastomer and a silicone rubber either alone or in combination, hence this pliable tip portion is low in physical strength and resistance to solvents and has a defect of such portion being subject to damage during infusion of a contrast media or its tip portion being dissolved depending on the kind of a solution infused.
Especially, it is often the case that the pressure which is imposed upon the catheter inner wall is about 100 PSI or even more when a contrast medium is infused, this being too high for such catheter to withstand.
Further, it is necessary to increase a wall thickness of a tube for insufficient strength because of its material being poor in physical strength, this resulting in a decreased inner diameter of the catheter. Moreover, since the material of the tip portion is elastic, this portion tends to elongate in the axial direction of its shaft and in the case of a fine peripheral blood vessel, the tip portion elongates and is broken as a guiding wire is worked therein, this resulting in a fault of the guiding wire not usable for helping insertion of a catheter into a fine peripheral blood vessel.
Meanwhile, conventional catheters with a part of their shaft being of porous structure so far developed are those which are safe from injuring the inner wall of a blood vessel with their tip portion pliable or which are capable of gradually discharging a curative drug solution through the portion of the porous structure, but no catheters possibly inserted into a fine peripheral blood vessel have been developed yet.
The catheter disclosed by the above-mentioned Japanese Patent Laid-Open Publication No. 2-142576 is not a microcatheter for infusion usable for fine peripheral blood vessels, being simply with its tip portion made pliable to be safe from injuring the inner wall of a blood vessel as is apparent from the "Object of the Invention" and from the description "those 1.5 to 3 mm in outside diameter, 1.0 to 1.8 mm in inside diameter and 0.3 to 0.6 mm in wall thickness are practical." The catheter disclosed by the above-mentioned Japanese Patent Laid-Open Publication No. 2-107268 is an intra-abdominal retention tube being pliable to be readily adaptable to the form of abdominal cavity when it is retained therein, and the excessive pliability disturbs its use as a microcatheter for insertion into fine peripheral blood vessels. Moreover, the catheter disclosed by the above-mentioned Japanese Patent Laid-Open Publication No. 60-51912 is comprised of a solid part and a porous part without any device for the insertion into fine peripheral blood vessels, and therefore, it is not used as a catheter for infusion for such fine peripheral blood vessels.
Hence, the present invention is to provide a microcatheter for infusion for solving the aforementioned problems and infusable into still finer peripheral blood vessels.
After intensive series of studies for the accomplishment of the aforementioned object, the present inventors have found that a microcatheter for infusion in which a tip portion of its shaft to be inserted into fine peripheral blood vessels is made pliable by the use of a porous wall tube having no communicating pores therein and is made smaller in outer diameter as well as wall thickness so as to be insertable into fine peripheral blood vessels by the aid of a guiding wire and/or on a blood stream and is imparted enough physical strength to withstand the pressure required for infusion.